The overall objective of the proposed research is to gain a better understanding of the control of the biosynthesis of deoxyribonucleoside triphosphages and the relationship between their control and the control of DNA synthesis. A key control exists in the first enzyme of this pathway, ribonucleoside diphosphate reductase. At present, our working model proposes that a protein which is synthesized constituitively and binds to DNA is used by an Escherichia coli cell to titrate DNA and when accumulated in excess is used to trigger initiation of DNA replication and also synthesis of ribonucleotide reductase. The proposed work will test the predictions of this model and will further elaborate the model. An in vitro coupled transcription-translation system will be used as an assay to purify the proposed protein. Also an in vitro assay for DNA initiation will be devised to show that the same protein is involved in both processes. The genetic region which contained the genes coding for ribonucleotide reductase will be characterized and sequenced. Studies will be conducted to investigate differences in the control of synthesis of ribunucleotide reductase in in eucaryotic cells. Finally, the in vivo reducing system used to couple NADPH oxidation to ribonucleotide reduction will be determined by using combination of various mutations.